Conventionally, Magnetic Resonance Imaging (MRI) apparatuses have popularly been used not only for morphological image diagnosis, but also for functional image diagnosis. More specifically, an MRI apparatus is capable of providing an fMRI image in which brain activities are expressed by using a method called “functional Magnetic Resonance Imaging (fMRI)” (see, for example, “Iyou Gazou Houshasen Kiki Handbook” edited by the Japan. Industries Association of Radiological Systems and published by Nago Bijutsu Insatsu Kabushiki Kaisha, 2001, pages 176-177).
The fMRI method is a method for generating the fMRI image in which activated areas of the brain are expressed by utilizing a Blood Oxygenation Level Dependent (BOLD) effect.
Next, the BOLD effect will be explained. In an activated area of the brain that has been activated by a movement or a stimulus, the blood flow rate increases, and also, because oxygen is supplied from the capillaries in the activated area to nerve cells, hemoglobin combined with oxygen (i.e., oxidized hemoglobin) is reduced so as to become reduced hemoglobin. In this situation, the degree with which the oxygen consumption amount of the nerve cells increases is lower than the degree with which the blood flow rate increases. As a result, the amount of oxidized hemoglobin in the venous blood within the activated area increases in a relative manner. In addition, oxidized hemoglobin is more difficult to be magnetized than reduced hemoglobin. In other words, the BOLD effect refers to a phenomenon where “in an activated area of the brain, the magnetic susceptibility decreases so that the intensity of the magnetic resonance signal changes”.
Accordingly, it is possible to specify a brain function activated site by generating a Magnetic Resonance Image (MRI) while an examined subject continuously and repeatedly performs a task for activating the motor area, the visual area, the auditory area, the language area, the sensory cortex, and the like, with intermissions of resting periods each called a “rest” and by comparing images corresponding to task periods with images corresponding to rest periods. In addition, by comparing images that have been taken, for example, while tasks that have mutually-different contents are being executed, it is possible to specify a site that is activated during all the mutually-different tasks in common with one another and to specify a site that is peculiarly activated during each of the mutually-different tasks.
An example of an image analyzing process to specify a brain function activated site can be explained as follows: First, an average image of all the images during the rest periods and an average image of all, the images during the task periods are obtained. Subsequently, a “t-test” is performed for determining a statistically significant difference based on a difference value and a standard error between the two population mean values with respect to the two average images, so that a “t-value image” is generated as an fMRI original image. Further, a linear correlation coefficient is calculated, and also, a correlation coefficient between pixel values of the fMRI original image and a reference function is calculated, so that a correlation coefficient image is generated as an fMRI image.
In this situation, a setting for the lengths of the time periods during which the rests and the tasks are executed is designed with blocks that are arranged with predetermined intervals. More specifically, as shown in FIG. 11, the setting for the lengths of the time periods during which the rests and the tasks are executed is expressed with a designed formation in which model blocks including rest-period blocks for having a rest and the task-period blocks for activating the brain are arranged along the time series. Thus, the setting is called a “block setting”. FIG. 11 is a drawing for explaining an example of the block setting.
A block setting process is performed by an operator who is a medical doctor or the like by inputting, as parameters, numerical values such as the quantity of rest-period blocks and task-period blocks and the number of times the rests and the tasks are repeatedly executed, together with the type of the task. For example, the parameters are input by using, as shown in FIG. 11, temporal phases (hereinafter, “phases”) that are expressed by using a repetition time (hereinafter, a “TR”) as a unit. Further, the block setting is used during an image analyzing process, which is performed after the images during the rest periods and the task periods have been collected.
In the current circumstances, there are often situations in which it takes a certain period of time for the brain to be activated after being stimulated, depending on the stimulus applied to the examined subject.
According to the conventional technique described above, however, the fMRI image is generated by using the data that has been collected during all the task periods and all the rest periods, while excluding the data obtained immediately after the collecting process is started. As a result, a problem remains where, even by referring to the fMRI image, it is not possible to understand, from the image, the manner in which the brain function activated site changes over the course of time.